Add is_pic field to statedump soinfo event

This field indicates whether the executable or library is position
independent code (PIC). The field is not added to the similar dlopen
event from liblttng-ust-dl because in that case all dlopened libraries
are necessarily PIC.

This allows a posteriori analyses to be performed without having to
read the executable file to know whether adresses are relative to the
base address or absolute.

Signed-off-by: Antoine Busque <abusque@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>